Question 1142572
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Here is an alternative to the standard algebraic method for solving mixture problems like this.  If you understand it (and if an algebraic solution is not required), it will get you to the answers to problems like this much faster and with much less effort.<br>
(1) the difference between the 6% and 12% of the two ingredients is 6%; the difference between the 6% of the first ingredient and the 7% of the mixture is 1%.<br>
So the 7% target concentration is 1/6 of the way from 6% to 12%.<br>
That means 1/6 of the mixture needs to be the ingredient with 12% vinegar.<br>
ANSWER: 1/6 of 240ml = 40ml of 12%; the other 5/6 of 240ml, or 200 ml, of 6%.